This invention relates to computer systems and more particularly to an apparatus for handling and storing optical disk cartridges. Even more particularly this invention relates to Error Recovery within such apparatus.
An optical disk is a data storage medium which is readable by a laser-based reading device. Optical disks known as "compact disks" or "CDs" have become increasingly popular during the past few years for recording music and audio-visual works. Due to the huge storage capacity of optical disks as compared to conventional magnetic storage media, optical disks known as "ROM disks" have become popular for storing computer readable information. Recent technology has produced optical disks which can be written as well as read by the computer, thus, in the future optical disks are expected to become increasingly more important in the computer industry and may eventually replace magnetically readable and writable storage media such as "floppy disks" and "hard disks." Another recent development, the ability to provide data storage on both surfaces of an optical disk, has effectively doubled the optical disk storage capacity.
Optical disks of the type used in computer applications are generally mounted in cartridges, and the reading devices generally read or write data through a slot provided on a surface of the cartridge. Currently, most optical disks are hand-inserted into disk readers. However, for large databases consisting of many optical disks, it is preferable, and perhaps essential, to provide an optical disk storage system for storing the disks at known locations, and an optical disk handling system which is capable of retrieving a desired disk from a storage location and inserting the disk into an optical disk reader. In a disk storage system wherein the stored disks and an associated disk reader are arranged in a longitudinally extending, two-dimensional array consisting of vertically extending columns and laterally extending rows, it is necessary for a disk handling system to be capable of engaging a disk, moving it vertically, laterally, and longitudinally and then releasing it in order to remove it from storage, move it into aligned relationship with the disk reader, and insert it into the disk reader. It may further be necessary for the disk handling system to flip the disk to reverse the side thereof which will be positioned in readable relationship with a reader. It may also be necessary to reorient a disk at the time it is initially inserted into the system by an operator.
Any system involving mechanical movement is subject to variations of such movement, and therefore subject to errors in the movement, called physical errors. These variations are caused by friction variations from mechanism to mechanism, lubrication variations, electrical power fluctuations, and many other causes. Most of the errors are of a temporary nature, and can be corrected by repeating the movement, or re-calibration and then repeating the movement, or by counter movements that reverse an undesirable condition.
Another type of error condition that can arise in such a system is a logical error. A logical error occurs when the state of the device is different from the state known to the host computer system using the device. For example, a cartridge is located in a magazine, or slot, different from the location identified in the host computer system. Another example would be an empty slot that is identified by the host system as having a cartridge.
Prior art devices have generally attempted to recover errors by re-initializing the mechanisms of the device to a known state, then attempting the failed operation a second or subsequent times. Sometimes this is unsuccessful because the failed operation was partially completed, and cannot be performed in the same way again. This problem is exacerbated when the failure is due to a loss of electrical power, since the contents of the device memory is lost, causing the machine to lose track of the operation that was being performed.
There is need in the art then for a system that detects and corrects temporary physical errors. There is a further need in the art for such a system that corrects certain logical errors. Still another need is for such a device that uses knowledge of the failed operation to direct error recovery. Yet another need is for such a device to retain, through an electrical power removal and restoration cycle, a record of the last operation attempted.
Various features and components of such a cartridge handling system are disclosed in U.S. patent applications:
(A) Ser. No. 278,102 filed Nov. 30, 1988 for OPTICAL DISK HANDLING APPARATUS WITH FLIP LATCH of Methlie, Oliver, Stavely and Wanger; now U.S. Pat. No. 4,998,232. PA1 (B) Ser. No. 288,608 filed Dec. 22, 1988 for OPTICAL DISK INSERTION APPARATUS of Christie, Wanger, Dauner, Jones and Domel; now U.S. Pat. No. 5,062,093. PA1 (C) Ser. No. 289,388 filed Jan. 18, 1989 for LATERAL DISPLACEMENT CONTROL ASSEMBLY FOR AN OPTICAL DISK HANDLING SYSTEM of Wanger, Methlie, Stavely and Oliver; and PA1 (D) Ser. No. 305,898 filed Feb. 2, 1989 for OPTICAL DISK CARTRIDGE HANDLING APPARATUS WITH PASSIVE CARTRIDGE ENGAGEMENT ASSEMBLY of Wanger, Methlie, Jones and Stavely; now U.S. Pat. No. 5,014,255. PA1 (E) Ser. No. 326,572 filed Feb. 28, 1989 for CARTRIDGE HANDLING SYSTEM of Wanger, Methlie, Christie, Dauner, Jones, Oliver, and Stavely, now U.S. Pat. No. 5,043,862. PA1 (F) Ser. No. 326,146 filed Mar. 19, 1989 for MECHANICAL SENSE OF TOUCH IN A CONTROL SYSTEM of Oliver, Wanger, Stavely, Methlie, Bianchi, Kato, and Proehl, now U.S. Pat. No. 5,040,159. PA1 (G) Ser. No. 334,665 filed Apr. 6, 1989 for CALIBRATION OF A CARTRIDGE HANDLING DEVICE USING MECHANICAL SENSE OF TOUCH of Oliver, Bianchi, Wanger, Stavely, and Proehl, PA1 (H) Serial No. 07/422,313 filed Oct. 16, 1989 for INPUT/OUTPUT COMMUNICATION BETWEEN AUTOCHANGER AND DRIVE of Wanger, Bianchi, and Proehl,
which are each hereby specifically incorporated by reference for all that is disclosed therein.